The present disclosure relates generally electric motor drives and, more particularly, to a motor drive topology having a built-in power failure tolerant capability when implemented in a dual voltage system such as a dual voltage motor vehicle.
In certain motor vehicle systems, such as electric power steering systems, steer and brake by wire systems, electric caliper systems and the like, both hardware and software redundancies are commonly implemented to provide a desired fault tolerant capability. A tradeoff, however, to such redundant features is the cost penalty associated therewith. For example, an electric motor used in a motor vehicle system (such as mentioned above) may utilize both a primary power source, as well as a backup power source to improve the fault tolerant capability.
With dual voltage electrical systems being developed for future motor vehicles, such as the emerging 14 Volt/42 Volt system for example, the opportunity exists for using both of the dual voltage supplies to provide power to redundant systems, including those systems employing electric motors. Accordingly, in the event of a failure of one of the power sources, a motor could maintain its operation through the surviving power source. At present, however, this would be accomplished through traditional methods such as including additional power switching or backup circuitry. The backup circuitry may even require a separate DC to DC converter for the transition between power supplies. Although this approach to system redundancy increases overall system reliability, additional hardware is used thereby driving up the total cost of the system.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a dual voltage motor drive and associated configured circuitry for power failure tolerance. In an exemplary embodiment, the motor drive includes a rotor assembly, rotatingly disposed within a stator assembly, and a plurality of motor phase windings configured to be energized in a determined sequence to cause a rotation of the rotor assembly. The plurality of motor phase windings are divided into a first group of windings selectively energized by a first voltage source, and a second group of windings selectively energized by a second voltage source, wherein the motor remains operational in the event of a failure of one of the first and second voltage sources.
In a preferred embodiment, the first group of windings is cross coupled to the second voltage source and the second group of windings is cross coupled to the first voltage source. In addition, a first capacitor is connected in parallel with the first voltage source and a second capacitor is connected in parallel with the second voltage source. Thereby, the second capacitor is charged by current flowing through the first group of windings, while the first capacitor is charged by current flowing through the second group of windings.
In one embodiment, both the first and second group of windings include at least one bifilar winding, wherein each bifilar winding includes a primary coil and a secondary coil, the secondary coil being magnetically coupled to the primary coil. The primary coil in each bifilar winding is energized by applying a phase control signal to a gate of a transistor connected to the primary coil, thereby causing an input current to flow through the primary coil in a first direction. Responsive to the removal of the phase control signal, the secondary coil in each bifilar winding has an output current flowing therethrough in a second direction opposite to the first direction. Each secondary coil in each bifilar winding further has a diode connected thereto, thereby preventing the flow of current through each secondary coil in the first direction. The first and second capacitors are charged by the output current flowing in the secondary coils of the bifilar windings.